This application claims the priority of German patent number 197 30 403.6-13, filed Jun. 16, 1997, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a multi-cylinder air-compressing injection-type internal-combustion engine.
As a rule, air-compressing injection-type internal-combustion engines are operated with a high excess of air; that is, there is a lean mixture quality, in the case of which the lambda ratio of the actual air quantity to the air quantity required for the combustion of the respect fuel quantity is larger than 1. In the case of a fuel combustion with a high air excess and at high temperatures, a high nitric oxide fraction is generated in the exhaust gas.
It is known from European Patent Document EP 0 58 016 A1, among others, to reduce the nitric oxide in that it is first stored in an absorber catalyst and is desorbed and reduced in cyclically following generation phases. In the regeneration phases, which as a rule are clearly shorter than the adsorption phases, an exhaust gas is required in front of the nitric oxide absorber catalyst which ensures the reducing conditions on the active surfaces of the exhaust gas after treatment device. As a rule, exhaust gas is used for this purpose which is free of oxygen and enriched with hydrocarbon.
In order to obtain, in the case of an air-compressing injection-type internal-combustion engine, with a defined operation point which is held constant, an exhaust gas which is free of oxygen, the combustion must already be designed for a minimal air-fuel ratio. As a rule, this is achieved by means of an intentional deterioration of the specific fuel consumption in that the injected fuel flow rate is raised and simultaneously the air flow rate of the cylinder charge is lowered. It is known from European Patent Document EP 0 621 400 A1 to raise the fuel flow in that, at a late point in time, more fuel is injected and thus a late position of the combustion is achieved. The air flow of the cylinder charge can be reduced in that the combustion air and/or the exhaust gas flow is throttled and/or a portion of the exhaust gas is returned into the intake pipe. In the case of a portion of the cylinder filling, the exhaust gas return device replaces the fresh air with a 21% oxygen fraction by exhaust gas with a lower oxygen content. For this purpose, the exhaust gas return rate, that is, the ratio of returned exhaust gas to the overall charge in the cylinder or the ratio between the fresh air and the residual gas in the cylinder should be as high as possible. According to the operating point, exhaust gas return rates of above 40% are achieved in practice.
In order to intensify the reducing effect of the exhaust gas, it is expedient to raise the content of reducing agents, for example, of hydrocarbons which are obtained from the diesel fuel. Generally, this can be achieved in that more fuel is injected into the cylinders than can be burnt by the air charge. It is also known from the above-mentioned European Patent Document EP 0 621 400 in the case of air-compressing injection-type internal-combustion engines to inject in a delayed manner a portion of the fuel after the main injection for this purpose. The late injection significantly increases the fraction of unburnt hydrocarbons in the exhaust gas.
When exhaust gas enriched with hydrocarbon is admixed to the intake air by the exhaust gas return device, however, after the start of the ignition of the main injection, the ignition delay is always shortened and, mainly for this reason, the point of concentration of the combustion is displaced in the earlier direction. As a result, the desired effect of a late combustion position is partially canceled again.
A goal of the invention is to increase, in the case of an air-compressing injection-type internal-combustion engine with an exhaust gas return device, the hydrocarbon fraction in the exhaust gas by means of a reinjection and of reducing the oxygen fraction.
This and other goals have been achieved according to the present invention by providing an air-compressing injection-type internal-combustion engine, comprising: an air intake pipe; a plurality of cylinders communicating with said air intake pipe, each of said cylinders communicating with respective exhaust gas pipes, said exhaust gas pipes being divided into at least two exhaust gas flows which extend separately from one another at least along a distance; an increased hydrocarbon emission being selectively generated is exclusively in the cylinders corresponding to a first of said flows; a second of said flows being communicable with said air intake pipe via an exhaust gas return device; and a nitric oxide adsorber catalyst.
These and other goals have also been achieved according to the present invention by providing a system for controlling the exhaust gas of an air-compressing injection-type internal-combustion engine, comprising: an air intake pipe; a plurality of cylinders communicating with said air intake pipe; at least two separate exhaust gas conduits communicating with said cylinders, a first one of the exhaust gas conduits communicating with at least a first one of the cylinders, a second one of the exhaust gas conduits communicating with at least a second one of the cylinders, said at least a first one of the cylinders being mutually exclusive from said at least a second one of the cylinders; a control device which selectively generates an increased hydrocarbon emission exclusively in said at least a first one of the cylinders; an exhaust gas return device arranged in said second one of the exhaust gas conduits and controllable to selectively divert at least a portion of an exhaust gas flow through said second one of the exhaust gas conduits to said air intake pipe.
These and other goals have also been achieved according to the present invention by providing a method for controlling the exhaust gas of an air-compressing injection-type internal-combustion engine having an air intake pipe and a plurality of cylinders communicating with said air intake pipe, said method comprising: communicating at least two separate exhaust gas conduits with said cylinders, a first one of the exhaust gas conduits communicating with at least a first one of the cylinders, a second one of the exhaust gas conduits communicating with at least a second one of the cylinders, said at least a first one of the cylinders being mutually exclusive from said at least a second one of the cylinders; selectively generating an increased hydrocarbon emission exclusively in said at least a first one of the cylinders; controlling an exhaust gas return device arranged in said second one of the exhaust gas conduits to selectively divert at least a portion of an exhaust gas flow through said second one of the exhaust gas conduits to said air intake pipe.
According to the invention, the exhaust gases of some cylinders are used exclusively for the exhaust gas return device, while, in the remaining cylinders, an increased hydrocarbon emission is generated at times. The exhaust gases are correspondingly distributed separately from one another to exhaust gas pipe with at least two flows. The separation of the two exhaust gas flows must be maintained at least to the exhaust gas return device so that no exhaust gas enriched with hydrocarbon arrives in the intake pipe of the internal-combustion engine. As a result, it is ensured that the effect of an overapportioned or delayed fuel injection is not canceled by a premature ignition.
Expediently, the hydrocarbon emission is achieved by an incomplete combustion in the corresponding cylinders in that, controlled by an electronic system of the engine, a fuel excess and/or a portion of the fuel is injected in a delayed manner.
In the case of internal-combustion engines with an exhaust gas turbocharger, it is expedient to guide the flows of the exhaust gas pipes separately to the turbine housing which expediently has a two-flow construction. Only in the confluence space of the exhaust gas turbine, the exhaust gas flow enriched with the hydrocarbon is guided together with the exhaust gas flow of the other flow which was not used for the exhaust gas return device.
In order to be able to optimally utilize the effect of a shock-type charging, it is expedient for cylinders with a maximal spark gap to be combined to one flow.
If the number of cylinders is uniformly distributed to two flows, the exhaust gas return rate is limited to maximally 50% depending on the available pressure gradient. A higher exhaust gas return rate or a larger exhaust gas quantity enriched with hydrocarbon can be achieved by a non-uniform distribution of the cylinders to the flows.
In order to be able to adapt the ratio between the exhaust gas return rate and the exhaust gas quantity enriched with hydrocarbon to the operating conditions, it is expedient to provide more than two flows, of which at least one is alternately assigned exclusively to cylinders for the exhaust gas return without enrichment with the hydrocarbon or exclusively to cylinders with a temporary enrichment with hydrocarbon. By means of a multi-flow construction, the shock-type charging effect is also improved.